How thick are walls?

Please don't draw plans with walls that are a single line thick. It looks stupid.

Find out how thick something is, and if you don't know and can't find out quickly, assume the following:

Most external walls are a minimum of 300mm thick.
Most walls separating different dwellings or tenancies (those requiring acoustic attenuation) are about 200mm thick.
Most internal walls inside a dwelling are approximately 100mm thick.